Experimental work done to date indicates that Optoacoustic Tomography will provide breast images with greater contrast and sensitivity to cancer than the currently preferred methods. In a Laser Optoacoustic Imaging System (LOIS), short, near-infrared laser pulses are preferentially absorbed by breast tumors. As a result, pressure waves are generated at the absorption sites. These propagate to the surface where they can be detected with ultra-wideband ultrasonic transducers. Computer processing of the detected signals results in an image in which contrast is largely determined by the tissue blood content. Cancerous tumors are blood rich because they develop a dense network of leaky blood vessels through the process of angiogenesis. The contrast in an optoacoustic image is significantly higher than that in images acquired with x-rays or ultrasound. Imaging with 2 different laser wavelengths can provide diagnostic information. Images taken with a wavelength of 1064 nm are particularly sensitive to the distribution of oxygenated blood. Images taken with a wavelength of 760 nm are more sensitive to the distribution of deoxygenated blood. Combining and/or comparing the two types of images yields a means for differentiation between cancerous and non-cancerous lesion. LOIS is suitable for examination of the breasts of all women, regardless of their age or skin color. The overall goal of this project is to develop a commercial prototype optoacoustic imager. The work of the Lasersonix team during Phase II will focus on incorporation of the components developed in Phase I into a complete 2D imaging system called LOIS-2D. LOIS-2D will be tested with 24 patients with suspicious breast lesions to verify the proper performance of the equipment and to perform initial tests of its diagnostic capability in collaboration with UTMB. The commercial prototype of a 3D optoacoustic imager, LOIS-3D, will be designed, developed, and fabricated. Specifically, a three-dimensional transducer array will be produced. The electronics and software will be modified to handle an increased number of detectors. The number of electronic channels that can be processed in parallel will be increased to 128. Image reconstruction will be performed in hardware. 3D images will be reconstructed in close to real time through a computer fusion of 20 images produced in real time.